Friday, June 26, 1998 Published at 04:07 GMT 05:07 UKWorld: Middle EastUS 'frustrated' over Saudi bomb probeThe force of the blast ripped off one side of the buildingThe US authorities say they are frustrated over the lack of progress in the investigation into the bombing of a military complex in Saudi Arabia two years ago which killed 19 US servicemen and injured hundreds more.

A spokesman for the Defence Department, Kenneth Bacon, answering questions from journalists on the second anniversary of the attack, said: "We are frustrated with our inability to bring this investigation to a close."

The blast was caused by a truck bomb parked outside the Khobar Towers building in the eastern Saudi city of Dhahran.

The force of the explosion ripped off one side of the building.

Since then, there have been signs of difficulties between the US and Saudi authorities regarding the investigation into the attack.

Last year, the US Attorney-General Janet Reno said the Saudi government had failed to turn over important information relating to the blast.

Efforts to find the perpetrators also faltered when a key suspect who agreed to co-operate with the FBI then changed his mind.

The New York Times reported on Sunday that the investigation into the attack was close to collapse after the FBI pulled out dozens of investigators who were sent to Saudi Arabia in the aftermath of the explosion.

The paper reported that the both sides were accusing the other of refusing to share information.

The case has been complicated by the sensitive nature of relations between the US and oil-rich Saudi Arabia, a key western ally in the Middle East.

Following the attack, there were suggestions that Iran might have been behind the bombing, but so far no conclusive evidence to that effect has been provided.

Earlier this year, the Saudi authorities suggested that Saudi dissidents might have been behind the blast.